YANGON, Feb. 8 (CNA) - Myanmar's generals issued a stern warning against further protests on Monday (Feb 8) as a mass uprising against their coup gathered pace, with hundreds of thousands on the streets demanding the release of ousted leader Aung San Suu Kyi.

The junta has so far refrained from using deadly force to quell the demonstrations sweeping most of the country, but with pressure building, riot police fired water cannon in an attempt to disperse thousands gathered on a highway in the capital Naypyidaw.

The military last week detained Aung San Suu Kyi and dozens of other members of her National League for Democracy (NLD) party, ending a decade of civilian rule and triggering widespread international condemnation.

In the face of an increasingly bold wave of defiance rippling across the country, state broadcaster MRTV warned that opposition to the military takeover was unlawful and signalled a potential crackdown.

"Action must be taken according to the law with effective steps against offences which disturb, prevent and destroy the state's stability, public safety and the rule of law," said a statement read by an announcer on the channel.

Tens of thousands of people rallied over the weekend in the first major outpourings of opposition, and the movement built on Monday with bigger protests in key locations across the country, as well as the start of a nationwide strike.

In Yangon, the nation's commercial capital, massive throngs spilt onto the city's main roads, immobilising traffic across the city and dwarfing the previous day's crowds.

"Down with military dictatorship" and "release Daw Aung San Suu Kyi and arrested people", the protesters chanted, flashing the three-finger salute that has come to symbolise their movement as car horns were honked in support.

Calls for a nationwide strike had gathered momentum over the weekend, with textile workers, civil servants and railway employees walking off the job in the commercial hub.

"This is a work day, but we aren't going to work even if our salary will be cut," one protester, 28-year-old garment factory worker Hnin Thazin, told AFP.

Construction worker Chit Min, 18, joined the Yangon rally saying his loyalty to Aung San Suu Kyi outweighed immediate concerns about his financial situation.

"I am jobless now for a week because of the military coup, and I am worried for my survival," he told AFP.

Similarly large crowds marched in Mandalay, the second-largest city and former seat of the country's pre-colonial monarchy, many clutching photos of Aung San Suu Kyi and waving the red flags of her NLD party.

Police attempted to disperse thousands of people gathered on a highway in Naypyidaw, where Aung San Suu Kyi is believed to be detained.

Water cannon was fired into the crowd, injuring at least two demonstrators, according to a photographer on the scene.

Huge rallies were also reported across much of the country, from Muse on the Chinese border to the southern cities of Dawei and Hpa-an.